P1135/p0125 error code on a 2000 4 runner

Hey All, new to the forum and the 4 runner community. Glad to be here. Recently picked up a 3rd gen 2000 series 4Runner in beautiful shape. About a week ago it started reading a p1135/p0125 error codes. From my research I was told to replace the B1 S1 o2 sensor. I did that today and cleared the code and it was back within 1 mile. Any ideas? It’s driving me insane.

if it matters, it’s a 2000 5speed.

 

Just in case bank 1 is driver’s side. Look for any exhaust leaks before the sensor. Sometimes a blown out gasket will cause unmetered air to enter the system and confuse the readings, causing a false code. Do a cold start and look under the truck for at spots on the exhaust at the connections.

 

That code p1135 seems to indicate you have a wiring issue. Usually you get a different code if the sensor is going bad but still able to be read by the ECU.

P0125...sounds like your temperature sensor is bad or you have a bad thermostat.